Pressure sensitive adhesive tapes, or adhesive tapes, are often provided in roll form, wherein the tape construction includes a backing, an adhesive layer on one major side of the backing, and a release layer on the other major side of the backing. The release layer allows the tape to be unwound from the roll at a controlled level.
Other articles having release characteristics are employed in a variety of applications. Any adhesive coated article, including tapes, die-cut adhesive articles, labels, and the like, require, as a matter of practicality, a release coating or a separate release liner. The release coating or liner provides a surface to which the article does not permanently adhere.
Duct tapes are a common and widely used type of adhesive tape. Duct tapes typically include a scrim, a polymer film backing, and an aggressive, rubber resin-based pressure sensitive adhesive that is coated over the scrim and the backing. The scrim provides strength to the tape and additionally allows the tape to be hand torn. Conventional melt blown polyethylene films used to make duct tape backings either do not contain a release material or employ low molecular weight release materials (e.g., waxes) that can bloom to the free surface of the backing and provide a release function. Without the use of release material, the unwind forces of duct tapes made with such films are extremely high due to the aggressive nature of the pressure sensitive adhesive employed. However, the low molecular weight release materials are cohesively weak and are not strongly bound to the film surface; therefore, the release material can transfer to the adhesive surface when the tape roll is unwound, resulting in reduced adhesion levels of the adhesive when applied to the target surface.
Conventional means to apply release layers on various articles, including but not limited to duct tape constructions, include solvent coating. Solvent coated release layers have been applied by dissolving the components in a solvent, coating the solution onto the targeted release surface, and drying to evaporate the solvent. One example of this approach is described by Dahlquist et al., U.S. Pat. No. 2,532,011. However, solvent based processes require a separate step to apply the release material, and further are of concern as a process typically requiring the use of volatile organic compounds (VOCs).
One non-solvent based approach to forming a release layer is extrusion or coextrusion of the release layer. That is, the release material is mixed with an extrudable polymer to form a release layer.
Berg, U.S. Pat. No. 7,897,666 discloses a silicone release material that can be added to an extrudable thermoplastic polymer. However, the additive requires the use of polyphosphoric acid as a binding agent, in order to impart non-migratory properties and prevent poor readhesion of the adhesive article.
Mohajer et al., WO 91/15538 discloses a release film including a base polymer and a silicone copolymeric additive such as a silicone polyamide or silicone polyurea.
Gardiner et al., U.S. Pat. No. 5,473,002 discloses a silicone additive that can be added to an extrudable thermoplastic polymer, the additive derived from silicone diamines and rosin isocyanates.
Bechtold et al., U.S. Pat. No. 7,105,233 discloses organosiloxane additives, wherein the additives are prepared by dehydrogenative coupling. The reaction results in the formation of Si—O—C linkages, which are known to be thermally and/or hydrolytically unstable and therefore unsuitable for extrusion processes.
Ohara et al., U.S. Pat. No. 5,213,743 discloses a method of making a release paper, wherein an alkyl modified silicone, or alkyl dimethicone, is melt blended with a polyolefin and extrusion coated onto a substrate. However, the blend must be post-treated, for example by heating the coated substrate for a period of 20 minutes, to cause the silicone to “bleed” to the surface in order to impart release properties.
There is a need in the industry to provide an extruded release layer, wherein release properties are provided without additional solvent coating, without provision of other additives, and without additional steps such as post-treatments. There is a need to provide release materials that concentrate sufficiently at the surface of the extrudate prior to solidification of an extruded layer in order to impart release properties thereto. There is a need to provide such release layers that do not transfer materials to the adhesive when it is contacted with the release layer.